281 



He perceived that whatever the gas* might be, in a current of which 

 was placed the thermometer with moistened bulb, the minimum or 

 stationary temperature of that thermometer must be attained when 

 just enough of heat was given out in cooling, by each new por- 

 tion of gas, to cause the evaporation of that new portion of mois- 

 ture with which this gas was at the same time saturated ; and that 

 thus the amount of depression would vary inversely as the spe- 

 cific heat of the gas, all other circumstances being the same. He in- 

 vestigated, however, the allowances that should be made for varia- 

 tions in such other circumstances, and took all other precautions 

 which his experience pointed out to be important. The consequence 

 has been a new determination of the specific heats of several different 

 gases, on which it seems that much rehance may be placed, from the 

 nature of the method, and from the aojreement of the partial results 

 with each other, and with those of Dr. Suerman, though some of 

 these results diff'er widely from those obtained by methods previously 

 employed ; the specific heat of hydrogen, for instance, being found by 

 Apjohn and Suerman, to be, under equal volumes, greater than that 

 of atmospheric air in the ratio nearly of seven to five ; whereas some 

 former experimenters had supposed it to be equal or inferior. And by 

 such results the law which had been thought to be obtained by a former 

 eminent observer, namely, that all the simple gases have, under equal 

 volumes, the same specific heat, appears to be overthrown. It is im- 

 possible not to feel some degree of regret, when we are thus compelled 

 to abandon a view which had recommended itself by its simplicity, and 

 had been found to be in at least partial accordance with facts ; but 

 besides that the search after truth is the primary duty of science, the 

 whole tenor of scientific history asssures us, that each new seeming 

 complexity, or apparent anomaly, which the study of nature presents, 

 is adapted ultimately to lead to the discovery of some new and 

 higher simplicity. 



A somewhat more distinct conception than the foregoing remarks 



* Dr. Suerman states, that M. Gay Lussac perceived that the specific heat of 

 any gas must be connected with the degree of cold produced by the evaporation of 

 a liquid placed therein ; but the remark appears to have been merely made in pas- 

 sing, and to have been afterwards neglected and forgotten. 



